I would say 744 - you can then go for a middle E/F pair of CW seats, ideally the last row which has the bassinet - one parent and toddler go in the middle, other parent goes on the D or G aisle seat facing off to the E/F pair with the infant on lap; bassinet can come out later in the E/F seat space - the E/F seat with the screens up will give you a mini "cabin" and during flight (when seat belts off) your toddler has a little space there to move around